The activation of myelin-reactive T cells is postulated to initiate the recruitment of pro-inflammatory Th1 T cells into the CNS of patients with MS. Accumulating evidence suggests that the induction of autoreactive Th2 T cells secreting IL-4 may provide a mechanism for the treatment of autoimmune disease. Altered peptide ligands (APLs) can deliver a lower strength of signal to T cells, resulting in differential cytokine secretion. Investigations by Kuchroo (Project 1) in the EAE model have shown that APLs induce a population of autoreactive T cells with a different fine specificity as compared to the T cells recognized the original self antigen and the T cells generated against APLs of PLP and MBP secrete IL-4 and suppress EAE. In patients with MS, we demonstrated that APLs of MBPp85-99 induce over IFN-gamma secretion in T cell clones. We will examine the mechanism of APL APLs of MBPp85-99 induce IL-4 over IFN-gamma secretion in T cell clones. We will examine the mechanism of APL induced cytokine switching in patients with MS. We hypothesize that APL may expand a small population of low-affinity autoreactive T cells specific for the self-antigen that are different from the pathogenic T cells, and thus generate regulatory effect functions with a different TCR repertoire upon encounter with the self antigen. This would be confirmed by the presence of different TCR sequences between APL and MBPp85-99 reactive T cells. The mechanism of actions of APL in patients with MS will be compared to the mechanism of action in rodents with EAE (Project 1). The ability of APL to differentially signal T cells suggest a mechanism of action for Copaxone (glatiramer acetate which decreases the attack rate in patients with MS. Whether the random amino acid structure of glatiramer acetate may make it a more cross-reactive will be tested in aim 2 using combinatorial peptide libraries. We hypothesize that glatiramer acetate can act as a unive4rsal weak agonist and differentially signal autoreactive T cells to secrete IL-4 rater than IFN-gamma. A prediction of this hypothesis is that the frequency of glatiramer acetate T cells recognizing combinatorial peptide libraries of 13 amino acids will be increased in patients after injections of glatarimer acetate. The use of combinatorial libraries with single fixed amino acid and variable amino acids at the other 13 positions can also be fixed to define the preferential antigens recognized by glatiramer acetate reactive T cells. MBPp85-99 and Copaxone reactive T cell clones will be examined to delineate the biochemical mechanisms for APL and Copaxone-induced alteration in TCR signaling specifically focusing on tintracellular signaling pathways that lead to activation of these nuclear factors, and differentiation of naive cells into those with distinct functions and cytokine profiles.